s
have been produced, either from one or from several allied species. Some
little effect may, perhaps, be attributed to the direct action of the
external conditions of life, and some little to habit; but he would be a
bold man who would account by such agencies for the differences of a dray
and race horse, a greyhound and bloodhound, a carrier and tumbler pigeon.
One of the most remarkable features in our domesticated races {30} is that
we see in them adaptation, not indeed to the animal's or plant's own good,
but to man's use or fancy. Some variations useful to him have probably
arisen suddenly, or by one step; many botanists, for instance, believe that
the fuller's teazle, with its hooks, which cannot be rivalled by any
mechanical contrivance, is only a variety of the wild Dipsacus; and this
amount of change may have suddenly arisen in a seedling. So it has probably
been with the turnspit dog; and this is known to have been the case with
the ancon sheep. But when we compare the dray-horse and race-horse, the
dromedary and camel, the various breeds of sheep fitted either for
cultivated land or mountain pasture, with the wool of one breed good for
one purpose, and that of another breed for another purpose; when we compare
the many breeds of dogs, each good for man in very different ways; when we
compare the game-cock, so pertinacious in battle, with other breeds so
little quarrelsome, with "everlasting layers" which never desire to sit,
and with the bantam so small and elegant; when we compare the host of
agricultural, culinary, orchard, and flower-garden races of plants, most
useful to man at different seasons and for different purposes, or so
beautiful in his eyes, we must, I think, look further than to mere
variability. We cannot suppose that all the breeds were suddenly produced
as perfect and as useful as we now see them; indeed, in several cases, we
know that this has not been their history. The key is man's power of
accumulative selection: nature gives successive variations; man adds them
up in certain directions useful to him. In this sense he may be said to
make for himself useful breeds.

The great power of this principle of selection is not hypothetical. It is
certain that several of our eminent breeders have, even within a single
lifetime, modified to {31} a large extent some breeds of cattle and sheep.
In order fully to realise what they have done, it is almost necessary to
read several of the many treatises